Alternative carpet-stretching devices are available that put less burden on the knees than this traditional knee kicker.
Overuse problems with carpet fitters
Knee problems in carpet fitters are a result of kneeling, use of a 'knee kicker' to stretch the carpet, and small traumas from sharp objects on the floor.
Conditions associated with this occupation include infrapatellar bursitis, osteoarthritis and occasionally patellar tendon rupture.
Bursitis from carpet fitting
There are two lubricating pockets (bursae) at the front of the knee that become irritated in occupations that require kneeling on the knee like a carpet-fitter - the infrapatellar bursa and the prepatellar bursa.
Each of these exist to allow the knee to bend without stretching the tissues. They are lined by a membrane of cells (synovium) which secrete lubricating fluid and the two sides of the bursa are normally able to slide against one another. If the bursa is repeatedly traumatised by kneeling, then the membrane will produce excess fluid and may become inflamed, which is called 'bursitis' and this will cause pain.
Osteoarthritis from carpet fitting
Another problem for carpetfitters may be early osteoarthritis of the knee.
"There is moderate quality evidence that longer cumulative exposure to kneeling or squatting at work leads to a higher risk of osteoarthritis of the knee."
"....In the UK this position is formally recognised, in that occupations where risks of OA knee are more than doubled (coal miners and carpet and floor layers under certain employment conditions) may qualify for no-fault State compensation...."
Other relevant links
Infrapatellar bursitis, Osteoarthritis, Patellar tendon rupture, Bursitis, Bursa